PRESSURE DEPENDENCY OF CANINE INTRARENAL BLOOD-FLOW WITHIN THE RANGE OF AUTOREGULATION

The mechanism of pressure-induced natriuresis remains controversial. T o assess whether intracortical or medullary renal blood flows (RBF) ch ange with changes in renal perfusion pressure (RPP), global and region al RBFs were measured using the dynamic spatial reconstructor, a fast computed tomography scanner, in eight anesthetized dogs (group B) with in the range of RBF autoregulation (RPP of 153.5 and 114.4 mmHg). Simi lar measurements were obtained in seven control dogs (group A) in whic h RPP was not manipulated. In group B, only inner medullary perfusion decreased (from 0.84 to 0.51 ml/min per cm(3) of tissue, P = 0.03) wit h reduction of RPP, whereas global renal, intracortical, and outer med ullary perfusions remained unaltered. In group A there was no change i n global or regional renal perfusion. The change in inner medullary pe rfusion in group B (-34.7%) was significantly different (P = 0.021) fr om that in group A (+27.4%). Global, cortical, and total medullary RBF s (ml/min) and volumes did not change in either group. These results s uggest that with changes in RPP, the only detectable change in intrare nal perfusion occurs in the inner medulla.